The present invention relates to a rope for operating (hereinafter referred to as a rope) particularly, this invention relates to a rope wherein a corrosion. More resistance is improved without lowering its durability for bending and a rope wherein the corrosion resistance is remarkably improved, each of which is preferably used for many technical fields such as a window regulator for an automobile.
A rope is generally produced by stranding a plurality of wire or by stranding a plurality of the rope (in this case the rope is called a strand). Such rope is sometimes corroded by, for example, water containing salt.
In order to prevent the rope from being corroded, the ropes mentioned hereinafter are proposed.
(a) A steel wire plated with zinc is drawn to obtain a wire for a rope. A plurality of the wires are stranded with each other and plated with tin to obtain a wire rope (Japanese Examined Utility Model Publication No. 25500/1979). PA1 (b) A steel wire plated with nickel or nickel alloy is plated with zinc or zinc alloy and is plated with tin or tin alloy on the zinc or the zinc alloy layer. Thus, what is obtained is a steel wire which is drawn and plurality of the steel wires are twisted to obtain a rope (Japanese Examined Utility Model Publication No. 10332/1990). PA1 (c) Steel wires plated with zinc-aluminum alloy are drawn and stranded with other to obtain an inner core for a control cable (Japanese Unexamined Patent Publication No. 212616/1990). PA1 b.sub.2 : outer diameter of the second side wire 45 of the core strand, PA1 c: outer diameter of the core wire 47 of side strand, PA1 d: outer diameter of the side wire 48 of side strand, PA1 D: measured outer diameter of rope 41. PA1 b.sub.1 : outer diameter of the first side wire 54 of core strand, PA1 b.sub.2 : outer diameter of the second side wire 56 of core strand, PA1 c: outer diameter of the core wire 58 of the side strand, PA1 d: outer diameter of the side wire 59 of the side strands, and PA1 D: measured outer diameter of the rope 51. PA1 b: outer diameter of the side wired 64 of the core strand, PA1 c: outer diameter of the core wire 66 of the side strand, PA1 d: outer diameter of the side wire 67 of the side strand, and PA1 D: measured outer diameter of the rope 61. PA1 T: wave diameter when the wire is loosed as shown is FIG. 16 (B).
The above-mentioned ropes and the inner cable for a control cable have an anti-corrosion property which has been improved as compared with a normal rope plated with zinc. However, with respect to the wire rope described in (a), the wire must be plated before a step for drawing a wire rod and after the step for stranding the wire, and a step for stranding the wire should be required. For that reason, a number of producing steps becomes rather numerous so that the cost for producing the wire rope is high.
With respect to the rope described in (b), three kinds of plating steps are required for producing the rope. Accordingly, producing steps increase remarkably.
With respect to the inner cable for the control of the wires is plated cable described in (c), each of the wires is plated with zinc-aluminum alloy. Accordingly, the cost for producing the inner cable is high.
On the other hand, for the purpose of improving the durability on bending fatigue of the rope, generally a diameter of the wire is made small in order to decrease the bending stress. Thereof, a tension strength is lowered due to the reduced diameter of a wire. In order to decrease the tension stress, the number of the wire is increased.
As the rope wherein means for improving the durability on bending fatigue is employed, the rope wherein a plurality of side strands are arranged around a core strand having a diameter larger than that of the side strand in such a state that the side strands are closed together is known as disclosed in Japanese Unexamined Utility Model Publication No. 64796/1987.
Further, the conventional rope has been closed in such manner that a tightening percentage is approximately in the range of 0 to 2% in order to prevent the wire from damaging when the strand is twisted. Researching the tightening percentage of available ropes for operating, the result was found that each tightening percentage of the ropes was in the range of 0 to 2%. In other words each tightening percentage was rather small.
Besides, the tightening percentage used in the specification for instance, with respect to the rope having 19+8.times.7 construction shown in FIG. 7 is obtained as follows: ##EQU1## where the calculated diameter is a sum of outer diameter of each wire and the measured diameter is a value which is obtained by measuring the diameter of a circumscribed circle of the rope.
Furthermore, it has been said that durability on fatigue property is improved when preforming is performed to the side strand so that a preforming percentage which is obtained by dividing the measured diameter into a wave diameter when the rope is loosed can be approximately in a range of 95 to 100% (page 185 of "a hand book of a wire rope" (Oct. 15, 1967) edited by the committee for editing a handbook of a wire rope published by Hakua Shobo).
As mentioned above, the rode having a stranded construction of, such as, the conventional rope wherein a plurality of strands are stranded is generally closed so that the tightening percentage is in a range of 0 to 2% and the preforming percentage is in a range of 95 to 100%.
Besides, the tightening percentage can be obtained by following former (1) with respect to the rope having 19+8.times.7 construction as shown in FIG. 7. ##EQU2## a: outer diameter of the core wire 43 of the core strand, b.sub.1 : outer diameter of the first side wire 44 of the core strand,
Further, with respect to the wire having W(19)+8.times.7 construction wherein the core strand is stranded so as to have a Warrington type parallel lay strand as shown in FIG. 8, the tightening percentage is obtained by following formula (2) ##EQU3## where a: outer diameter of the core wire 53 of the core strand,
On the other hand, the tightening percentage of a rope having 7.times.7 construction as shown in FIG. 9 can be obtained by following formula. ##EQU4## where a: outer diameter of the core wire 73 of the core strand,
Next, the preforming percentage .phi. is obtained by following formula (4). ##EQU5## where D: measured outer diameter of a rope as shown in FIG. 16 (A), and
However, in the conventional rope, the tightening percentage is small and the preforming percentage large; that is, in this rope each strand is not stranded so tightly and the rope which is not closed so tightly is subject to deformation in the radial direction of the rope when the rope is used in such a portion that the rope is bent while the rope is slid, for instance in a guide which cannot rotate. Accordingly, there is such a problem that the durability on bending fatigue is low, since the wire is subjected to secondary bending i.e. the wire is subjected to local bending due to an external pressure whereby the wire is pressed against the layer of the wires located innerly.
The object of the present invention is to provide a rope having the same corrosion resistance as that of the conventional wire rope wherein wire employs a steel wire by virtue of using a steel superior corrosion resistant wire for the the specific wire, the corrosion resistance of which is superior, and a rope wherein the endurance property for bending is superior and a cost for producing the wire is lowered. Further, another object of the present invention is to provide a rope wherein the endurance property for bending fatigue when the wire is subjected to bonding in sliding movement is remarkably improved, by virtue of specifying the the tightening percentage and the preforming percentage.